Field of the Invention
The present invention relates to a power-driven work tool comprising a shank, an engine provided at one end of the shank, and a working means connected by a hinge to the shank at a second end thereof and rotatable around at least one axis perpendicular to the shank, the engine driving the working means via a drive shaft extending through the shank.
A plurality of shank-mounted work tools of different types are used at present, such as clearing saws, grass and hedge trimmers, pruning saws, and the like. In such work tools, a working means is usually fixed to the shank which means that the operator must turn the whole shank and/or change his own position in order to be able to perform an intended working phase. Some working phases may yet be difficult to perform.
It has therefore been previously proposed to attach the working means to the end of the shank such that the working means is adjustable to different angular positions relative to the shank; see for instance W091/15944, U.S. Pat. No. 4,760,646 and U.S. Pat. No. 4,916,818. With this type of device, however, the operation must be interrupted to alter the angular orientation of the working means, and the working means must be secured at the new angular orientation by securing means provided on the working means. In the case of a pruning saw having a long shank, for example, it is a time consuming operation between cutting of two branches to bring the work means down to ground level, adjust the angular orientation of the work means relative to the shank, and then subsequently raise the work tool for cutting the next branch.
In previously known devices having an adjustable working means, various types of gearing have been used for transmitting driving torque across a hinge. This results in an increased weight and size of the work tool, which will therefore be more cumbersome and heavy in use.
In addition to this type of work tool, there are also work tools utilizing a tool shank having a complete work tool, i.e. comprising an engine as well as a working means hinged to one end of the tool shank. Unfortunately, this arrangement results in a heavy weight load at the outer end of the shank, and therefore makes operating the work tool very tiring. Examples of such devices are provided by U.S. Pat. No. 4,207,675 and GB-B 2266682.
In the device according to GB-B 2266682, the other end of the shank is provided with an extra counterweight in order to balance the weight of the tool. This means that the total weight of the work tool is at least tripled, considering the length of the levers on which the tool and the counterweight, respectively, are acting. Further, in this known work tool the tool is suspended in a pivotable cradle attached to the forward end of the shank which makes the work tool very cumbersome and difficult to use in narrow spaces.
The known work tools have either a shank of fixed length, which means that the working range is predetermined, or a telescoping shank. The telescoping parts of the shank are latched in a predetermined mutual position for each work phase, which means that the work must be interrupted for altering the length of the shank.